The problem involves 3 contracts with an interdependence as follows:
library --> ProductContract --> BillingContract
The contracts are structured as follows: (The DataSet.sol contract below is referenced from a solidity example from: https://github.com/chriseth/solidity-examples/blob/master/iterable_mapping.sol

library DataSet {   
  struct IndexValue { uint keyIndex; uint256 value;}  
  struct KeyFlag { uint key; bool deleted; }  
  struct KeyValue { uint key; uint value; }  

  struct Data {   
      mapping(uint => IndexValue) data;  
      KeyFlag[] keys;  
      //KeyValue[] kvpairs;
      uint size;  

  function insert(Data storage self, uint key, uint256 value) returns (bool replaced){  
    uint keyIndex = self.data[key].keyIndex;  
    self.data[key].value = value;  
    if (keyIndex > 0)  
      return true;  
      keyIndex = self.keys.length++;   
      self.data[key].keyIndex = keyIndex + 1;  
      self.keys[keyIndex].key = key;  
      return false;  

  function getCurrent(Data storage self) returns(uint index){  
      return self.size - 1;  



import "DataSet.sol";  
contract ProductContract {  
    using DataSet for *;  
    DataSet.Data d;  
    mapping (uint => uint) IDToVal;  
    function register (uint p_id, uint val) returns (bool registered) {  
        IDToVal[p_id] = val;  
        registered = true;  
    function getVal (uint p_id) returns (uint v) {  
         return IDToVal[p_id];  


import "ProductContract.sol";    
contract BillingContract {  
    ProductContract pc;  
    address PC_Address;  
    function BillingContract (address p) {  
        PC_Address = pc;  
        pc = ProductContract(p);  
    function getVal (uint p_id) returns (uint v) {  
        return pc.getVal(p_id);  

This results in an error on compiling:

Error: Library "DataSet" declared twice (will create ambiguities during linking).  
    library DataSet {
Spanning multiple lines.  
The other declaration is here: DataSet.sol:3:1: 
    library DataSet {   
Spanning multiple lines.
Compiliation failed. See above.  

There is a form of transitive dependence on the above contracts - when I try to use all the contracts in a single '.sol' file, the compilation occurs just fine. Is there a way in which the '.sol' files can be separated and compiled properly? Please advise!

  • What environment are you compiling in. I've had these dependancy stack issues before with older versions of Solidity in Browser Solidity, though I thought they been cleaned up. Try importing the library into BillingContract.sol also and see if it compiles
    – o0ragman0o
    Apr 2, 2017 at 4:02
  • I am using truffle v 3.x to facilitate the compilation of these contracts - using solidity ^0.4.4 (a higher version of solidity doest seem possible to use in truffle). Tried your suggestion, but still it results in the same error as above
    – skarred14
    Apr 2, 2017 at 7:45
  • Even after updating the solidity version to ^0.4.8, i see the same issue. I have out the dependent contract BillingContract.sol in the following order - still no resolution for the above error ``` import "DataSet.sol"; import "ProductContract.sol"; ```
    – skarred14
    Apr 2, 2017 at 17:15

1 Answer 1


I actually had similar issue in my contract and it was due to the fact that I did not include version pragma in the header :

pragma solidity ^0.4.4;

solved my problem.

hope it helps

  • Thanks! Tried 0.4.4, 0.4.6, 0.4.7 as well but to no avail. Doesn't look like its a compiler version issue
    – skarred14
    Jun 9, 2017 at 21:56

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